Animals, for example mice, are used extensively in the examination of gene function, the development of drugs, and in other laboratory research applications. Often, the animals are constantly moving around, making it difficult to examine them for measurements of physiological parameters. Because of the constant movement, for example, one cannot easily attach electrodes for measuring cardiac or muscle activity to the main body section of the animal. The electrodes placed on the chest area of a small animal can also hinder movement. In addition, the large and cumbersome electrodes may cause added stress to the mammal, and may further hinder their movement.
One physiological measurement that is often useful in research applications is the electrocardiogram (ECG). The ECG is of interest to pharmacologists interested in the effects of drugs on heart rate and ECG indices. However, to date there has been some difficulty in obtaining accurate ECG readings from animals without stressing the animal, or implanting devices within the animal using a surgical procedure. The stress on the animal must be approximated to compensate for different ECG results of the stressed versus unstressed animal. Such approximations decrease the accuracy of the ECG readings. In addition, the requirement of a surgical implant can be both too time consuming and too expensive to implement when dealing with larger volumes of animals. Further, there has been some difficulty in obtaining ECG readings while the animal is moving (such as on a treadmill or in a cage).
A recent advance in the field of monitoring the ECG of small rodents non-invasively involves obtaining the required electrical signals through conductive electrodes upon which the small rodents stand. The electrical signals are obtained from the feet of the small rodent. When a small rodent is at rest, it is possible to record continuous signals. However, when the small rodent moves, the contact between the feet and the electrodes is interrupted and the ECG signal is lost. By splicing the signals as contact is re-established between the feet and the electrodes, the ECG signal is restored. However, if the small rodent is running, the stride frequency can exceed 8 Hz, such that the contact time between the foot and the electrode is less than 200 ms. The heart frequency in small rodents (e.g., a mouse) can be below 8 Hz. Thus, the interval between heart beats approaches 200 ms. Therefore, detecting ECGs through the feet of small rodents as they walk or run can be difficult.